CRYSTAL CHANNEL FILTERS 



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Considering again the filter schematic as a whole (Fig 3) and 

 neglecting the dissipation in the crystals and condensers, the filter may 

 be regarded as made of two lattice filter sections having ideal reactance 

 elements, that is, elements free from dissipation. The location of the 

 effective resistance of the coils outside the lattice, for purpose of per- 

 formance analysis, shows how at the end of the filter these resistances 

 may be regarded as part of the terminating impedance between which 



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-7 -6 -& -4 -3 -2 -I +1 +2 +3 +4 -1-5 



FREQUENCY FROM CARRIER IN KILOCYCLES 



Fig. 7 — In a lattice filter section transmission occurs for frequencies where the 

 impedances for the two arms of the lattice are of opposite sign and attenuation peaks 

 of very high loss occur where the impedances cross. 



the filter works, and how between the filter sections the resistances 

 may be combined with a shunt resistance to form a resistance pad 

 which matches the image impedance of the two filter sections. The 

 effect, then, of the coil resistances is primarily to provide a flat loss 

 over the entire frequency range and does not affect appreciably the 

 shape of the loss characteristic furnished by the reactance inside the 

 lattice sections. 



